Crevasses are dangerous, especially when traveling with machinery.
Avoid crevassed areas if possible, even if it entails making a considerable detour.
To date, no one in the USAP has been killed as a result of a snowmobile (skidoo) crevasse fall, but there have been numerous close calls. It's only a matter of time before a death occurs if greater attention is not given to safety. Personnel have been killed in a crevasse fall where snowmobiles were not involved.
Limited field testing has been carried out on the actual effectiveness of the methods described in this chapter. The results have been sobering in regard to the difficulty of stopping a fall, especially at speeds higher than 5 mph and/or with slack rope between the snowmobiles. The driver of a machine that falls in a crevasse is virtually assured of severe injury. This means that detection of crevasses and good route-finding to avoid dangerous areas are essential to safe travel.
Always have the capability to rope snowmobiles and drivers when traveling on a glacier. Be aware that glacial conditions vary enormously in Antarctica, from one year to the next. Glacial conditions can change in a few weeks in some areas of Antarctica.
In areas where there is any possibility of crevasses, roped travel should be used. It is often very difficult to detect crevasses . Stop and probe ahead if you're at all suspicious. Act conservatively and operate within a wide margin of safety.
Roped travel with snowmobiles should be practiced with an experienced person in a realistic area prior to beginning a trip. Make sure the Field Safety Training staff knows that you'll be traveling in areas that may be crevassed, and that you need to practice roped travel.
There are numerous systems for traveling through crevassed areas with roped snowmobiles and sleds, and safer options are always being sought. Please feel free to question the systems described in this chapter and provide constructive comments. The information provided here does not substitute for training or experience.
18.1a Aerial Reconnaissance
Aerial and satellite photographs provide an excellent source of information regarding crevasse locations. Direct aerial reconnaissance from the flight deck should include viewing proposed routes of travel from the air and marking the positions of crevasses on a map. Crevasses are more easily detected when the sun is at a low angle.
18.1b Tow Ropes
Tow ropes are used to connect the lead snowmobile to the sled(s) and/or snowmobile(s) behind it. Tow ropes are separate from, and in addition to, the safety ropes. Tow rope diameters of 3/4" to 1" (22-mm) nylon twisted rope are recommended. Twin 1/2" ropes (or larger) are a good alternative. In BFC field testing, Figure-8 knots tied every meter in the tow ropes, dramatically increased the fall-catching ability of the roped-snowmobile train.
The length (distance between snowmobile and sled) should be 15- to 20-meters. This length can be halved when you're not in a linked travel mode (i.e., when one snowmobile is pulling one sled and is not roped to another snowmobile).
The ends of the tow ropes should be tied with Figure-8 knots on a bight, or spliced to 5-ton shackles or locking steel carabiners.
A 1.5-meter-long protective sheath (PVC or rubber tubing) should be placed over the tow rope immediately ahead of where it secures to the sled or snowmobile its pulling. Secure the sheath with a piece of cord so that it can't move forward. This end of the tow rope will then be protected by the sheath should a sled or snowmobile run over it.
Attach the tow ropes to the snowmobiles and sledges with either 5-ton shackles or steel screwgate carabiners. (Don't use non-locking carabiners.)
Note: Engine vibration can unscrew the locking carabiners. Steel carabiners have failed under very light tow loads when the gate is unscrewed. Two steel carabiners with reversed gates will ensure a safer system. Secure carabiner screw gates and shackle pins with wire, tape, or rubber washers, etc. so that they won't unscrew.
18.1c Nansen Sled Back-up Rope
With Nansen sleds, it's necessary to loosely tie a back-up tow rope on the underside of the bridges. This rope should be 3/4" or 1" nylon twisted rope and should attach onto each end of the Nansen sled towing rope with the same shackle or carabiner that is used for towing. This back-up tow rope needs to be tensioned in such a way that it does not bear the load unless a large impact occurs.
18.1d Snowmobile Cables
All snowmobiles used for travel in crevassed areas should be fitted with a steel cable encircling the snowmobile. The 5-ton shackle on the tow rope must be fitted over this cable when hitching the snowmobile, to ensure that the snowmobile stays belayed to the tow rope in the event a crevasse fall pulls out the snowmobile's hinge plate.
18.1e Tether Switches
The tether switch is a thin line that runs from the snowmobile's kill switch to the driver's harness. This tether ensures that the snowmobile will stop (the engine is killed) if a driver falls from the machine. If the tether switch isn't used, the driver may end up hanging beside a spinning snowmobile track, which could cut the driver's rope or result in serious injury.
18.1f Driver Safety
When traveling linked, snowmobile drivers should kneel to one side, rather then straddling the seat, so in the event of a crevasse fall there is a better chance to jump or fall clear of the machine.
A series of pre-arranged hand signals should be used for communication between linked snowmobiles and sleds. Your field party should have signals for stopping, slower, faster, ok/ready-to-go, crevasse, and any others found to be necessary (i.e., "place flag here," etc.). The hand signals shown on the following page have been used effectively by past field parties.
18.1h Travel Speed
Linked travel requires continuous concentration, and is not suited for fast speeds. In BFC field tests, speeds over 5 mph dramatically increased the distance a snowmobile fell, and stopping the fall proved very difficult.
When traveling in linked formation, it is vital that you don't allow any slack to develop in the tow rope. Invariably this means that the lead snowmobile will at times be slightly pulling the trailing machines. A slack tow rope will continually be run over and will jam. If you drive over the tow ropes and safety ropes, the system will be compromised. The ropes may break under a load if one of the machines falls into a crevasse.
* [See figure ³ROPEDTR1²]
18.1i Crossing Crevasses
Stop and probe all crevasses to determine if they are safe to cross. Probing should be done by the driver of the lead snowmobile. A ski pole, without a basket, will suffice for a probe.
If you must cross a crevasse, always do it perpendicular to the line of the crevasse. If a snowmobile or sled starts to break through a snowbridge, experience and circumstances will dictate whether to brake and attempt to hold the fall, or continue driving forward in hopes of getting across before a catastrophic collapse of the snowbridge. In either case, a change of underwear is recommended.
18.1j Stopping a Fall
When stopping a fall into a crevasse, apply the brakes and, if possible, quickly kill the engine. The engine will be killed automatically if it's your snowmobile that's falling and you fall off the machine, thereby pulling the tether switch line.
In hard snow conditions, rope brakes on the sleds will increase friction and braking ability.
If you're a rider on a Nansen sled, and the sled is rigged for it, stand on the footbrake.
18.1k Travel on Foot between Snowmobiles and Sleds
In crevassed terrain, you must remain tied in when walking between your snowmobile and the other machines and sleds. Many a crevasse has been found by a driver stepping off their snowmobile (which has a lighter ground pressure than a person on foot), and breaking through a snowbridge that was crossed seconds before without incident by the snowmobile. To walk forward or back to another snowmobile or sled, you can self-belay with a prussik or ascender on your safety line or on a spare rope.
A good habit to get into when walking back and forth between machines and sleds is to straddle the tow ropes.
The prospect of falling into a crevasse on a snowmobile is extremely frightening. No system presently exists that allows the driver a guaranteed clearance from the snowmobile. There's a high probability of injury occurring to a falling driver. However, the following roping procedures will keep you as safe as possible in the event of a crevasse fall (see diagrams on the following two pages).
18.2a Front Driver
Clip the bitter end of an 11-mm climbing rope to your harness with a Figure-8 knot and locking carabiner. Use a prussik or ascender to fine tune the tension.
Walk the rope back to the sled or second snowmobile, tie a Figure-8 on a bight, and clip it into the front towing thimble with a locking carabiner. Coil the unused rope neatly and stow it on the sled.
If there's a rider on the sled, adjust the remaining portion of the rope, clip it to either the front or rear towing thimble of the sled, and then clip it into the rider's harness with a Figure-8 knot. Stow any extra rope out of the way.
Roping up will be much easier and quicker if you cut your safety ropes to the exact lengths needed before you go into the field. The BFC has bulk spools of climbing rope, and can provide assistance on the lengths you'll need.
* [See figures ³ROPEDTR2² and ³ROPEDTR3²]
Lead drivers should carry a 45-meter climbing rope in a stuff sack (throw-bag style) neatly stowed on the snowmobile. This can be used for probing out ahead of the machine, or to rescue others in the field party. Equip this rope with prussiks or an ascender next to the carabiner (or Figure-8 knot) used to hook onto the driver's harness.
18.2b Rear Driver
There are two recommended methods for tying in the second snowmobile.
Clipping In Behind: The easiest system to manage is to clip onto the back hitch of the snowmobile you're riding on. Secure the end of a 45-meter rope to your harness with a Figure-8 knot and a locking carabiner. Attach this with a locking carabiner (on a Figure-8 on a bight) to the back hitch of the snowmobile. Make sure the steel cable that encircles the snowmobile runs through the carabiner.
Secure the extra rope in a stuff-sack (throw-bag style) and neatly stow it on the rear of the snowmobile out of the way. The extra rope can be used for self-belaying away from the machine using an ascender, and will be handy for rescues. Clipping in behind the snowmobile makes rope management easier, but in a crevasse fall, the driver will be hanging below the machine. Self- rescue will be next to impossible.
Clipping In Ahead: Having the rear driver's safety line run ahead to the Nansen sled is potentially a safer system, but is harder to manage. Attach the end of the safety rope to the driver's harness (Figure-8 and locking carabiner). Take the line forward and attach it to the rear towing thimble on the Nansen sled with a locking carabiner. Use a prussik or ascender on the driver's harness to "fine tune" the distance. Neatly coil excess rope and stow it on the sled.
This system makes it possible for self-rescue by preventing the driver from falling below the snowmobile, and providing an immediate safety line for self-belaying up to the sled in front. However, it's very difficult to keep from running over the rope, especially in rough terrain (sastrugi).
Note: An experienced USAP field mountaineer prefers to run the safety rope from the rear driver to a 9-mm prussik wrapped on the tow rope just ahead of the protective tubing. This helps to not run over the rope and does not allow the driver to fall below the snowmobile.
Remember: It is highly probable that the secondary riders and/or drivers will be the ones that will fall through a weakened snow bridge.
Just as in roped-mountaineering, three snowmobiles roped together are safer than two. In BFC field testing, a roped-snowmobile train of three dramatically increased the ability to stop a fall quickly (two snowmobiles catching the third). Never travel with less than two snowmobiles and one sledge linked together, when traveling in crevassed areas. Depending on the size of your field party and the amount of cargo you're transporting, there are various travel configurations, which are illustrated on the following three pages.
* [See figures ³ROPEDTR4² and ³ROPEDTR5² and ³ROPEDTR7²]
See the diagram on the following page.
* [See figure ³ROPEDTR6²]
The following gear should be carried by each member of a field party traveling in crevassed areas. Equipment carried in the crevasse rescue bag is to be used in addition to the personal gear carried by each individual. A listing of the equipment in a crevasse rescue bag appears in Appendix E.
Personal Equipment (Each Person) 4 Prussiks: 2 Long and 2 Short 2 Slings: 1 Long and 1 Short 2 Pulleys 1 Figure-8 Descender 5 Carabiners 2 Locking Carabiners 1 Picket 1 Ice Axe
The figures on the following two pages show a Nansen sled and how to distribute the cargo load. Additional points on loading a Nansen sled follow.
* [See figures ³ROPEDTR8² and ³ROPEDTR9²]
On to Chapter 19: Glacier travel with heavy machinery.